This epidemiologic study is designed to determine if enteroadherent forms of E. coli are responsible for gastrointestinal disturbances occurring in former Mormon missionaries who have served the Church in developing countries. Salt Lake City presents a unique opportunity to study the role of enteroadherent E. coli in individuals who have lived in both developed and underdeveloped countries of the world, as the Church of Jesus Christ of Latter-day Saints sends missionaries into the field worldwide. The vast majority of these young men and women come from Utah and, upon return, often seek medical care at the University Medical Center. Twenty-one subjects have been studied as of the spring of 1999. In the first twenty-one individuals studied, enteroadherent E. coli was identified in only three. This was in sharp contrast to the 60% incidence discovered in a pilot study in which returning missionaries were evaluated within a month of returning to Salt Lake City. It was then recognized that most individuals enrolling on the study had returned from their missions four or more months before contacting the clinic. These findings prompted a revision in the study design by which enrollment of subjects occurs immediately upon return to the United States. Subjects for this study are those who had had persistent diarrhea in the three-month period before they left their mission assignments.